The present invention is related to solid state AC power switching, in general, and more particular, to a solid state relay for switching AC power to a load, including a reactive component, with reduced electromagnetic interference (EMI) or noise, and a method of operating the same.
With the increased use of electronic/computerized control and instrumentation systems on-board aerospace vehicles, it has become increasingly important to minimize the electromagnetic interference (EMI) or noise that is generated when switching AC power to electrical loads. Such EMI may have an adverse effect on the avionics, especially when generated over the AC power lines. Back-to-back solid-state switches, like field effect transistors (FETs), for example, have been used in solid-state relays (SSRs) for AC power switching in a variety of applications. Heretofore, these applications attempt to control the solid-state switches or FETs of the SSR simultaneously at zero voltage across the FET switches and/or at zero current therethrough. Due to inaccuracies of timing, exact switching at zero voltage and/or zero current is not effected which causes EMI to be inherently generated by the AC power switching. These timing inaccuracies are exacerbated when the power frequency is varying or unknown.
What is needed then is a solid-state relay that overcomes the drawbacks of the current solid-state relays by permitting AC power switcing with minimal generation of EMI. A solid-state relay that is not dependent on switching timing accuracy or constant or known power frequencies is highly desirable.